Keir is the Prince of the Unseelie Sidhe, which for them remains the highest title. This seems to have been done in desire to fully contrast against the Seelie structure. The Seelie are ruled by a Queen and some myths even have a King though the Queen is more significant, so the Unseelie chose to refuse even have those titles and remain with Prince and Princess, with the Prince being the primary power. Keir is full-blooded and the pride of many of the Unseelie. He is fiercely protective of his own kind, and has occasionally shown a somewhat cruel side in how he acts towards mortals. However, he also was quick to reveal that Fostismeras of the Seelie is in fact, his half-brother. They share a father (the previous Prince of the Unseelie), which means by right, Fostismeras is also technically an heir to the Unseelie throne if something happened to Keir or Keir has no offspring.

Keir did sanction the war against the Seelie, but it does not seem to be out of a particular bloodthirstiness. He has claimed the survival of his people depends on something that the Seelie currently possess, though only the higher power Seelie seem to have a guess as to what he means. Neither side are giving the answer. Keir seems to have ties to all the elements, but as his eyes turn from blood red to an ice blue when he gets angry, it is not surprising to see him often in use of mist and ice when he is truly angry. He seems to have an almost playful relationship with Uiruka, at least on his end, though Keir's teasing seems to exasperate Uiruka on occasion and even, surprisingly, fluster the general of the Unseelie armies.

Keir has not been strictly seen in any other form, though a black snake with blue eyes has been suspected of being the prince himself.

Did you know?

"Keir" is Gaelic for Black or Dark. "Nathair" is Gaelic for Snake. This contrasts with the image Fostismeras often takes of a golden serpent but shows that the serpentine form seems to run in their blood.